Zero thermal expansion in cubic MgZrF 6

Isotropic zero thermal expansion ( ZTE ) is rare but intriguing physical property in materials. Here, we report an isotropic ZTE property in a double ReO 3 ‐type compound of MgZrF 6 , which exhibits a negligible value of coefficient of thermal expansion (α l  = −7.94 × 10 −7  K −1 ( XRD ), α l  = −4.22 × 10 −7  K −1 (dilatometry), 300‐675 K). The ZTE mechanism of MgZrF 6 is understood by the joint studies of temperature dependence of crystal structure and lattice dynamics. Interestingly, different magnitudes of atomic displacement parameters ( ADP s) for the fluorine atoms in M Z rF 6 ( M  = Ca, Ni, Mg) are found. The strong temperature sensitivity of ADP s demonstrates intensive transverse thermal vibration of fluorine atoms, which contributes essentially to the negative thermal expansion of CaZrF 6 . By contrast, for NiZrF 6 with positive thermal expansion, the temperature response of ADP s is weak. Moderate transverse thermal vibration takes place in MgZrF 6 , and ZTE appears. Furthermore, lattice dynamics of MgZrF 6 is studied by temperature‐dependent Raman spectroscopy, which reveals the ZTE mechanism. In particular, the F 2g and A g modes, corresponding to the bending and stretching vibrations of fluorine atoms, respectively, neither soften nor harden over the whole temperature range, which is correlated with the isotropic ZTE property of MgZrF 6 .